1. Field of the Invention
The invention relates generally to systems and methods for determining the type of medium in cooking systems, such as a deep fat fryer.
2. Description of Related Art
Large capacity cooking devices (referred to herein as deep fat fryers, cookers, and the like) have been devised for cooking products in a heated or pressurized environment, or both. Such devices may include a cooking vessel, which may be filled with a cooking substance (e,g., oil or shortening) and heating devices surrounding or immersed in the vessel for heating the cooking substance. Food products to be cooked are placed in the vessel, either directly or possibly contained in a food product cooking container, and are cooked for a desired length of time.
Cooking devices may have several temperature control stages to effectively and efficiently heat a cooking substance. For instance, in "melt" mode, energy is pulsed into a solid or liquid cooking substance to heat it without burning it or scorching the cooking vessel. During "cook" mode, the temperature of the cooking substance may be thermostatically regulated to a cooking set-point temperature, so that heat may be applied for an extended period of time below the setpoint. These two stages may be separated by the melt exit temperature, which is the temperature at which the transition from melt mode to cook mode occurs.
After repeated use, these cooking devices require cleaning. For example, the cooking substance may be first be drained from the vessel, and the vessel filled with a cleaning substance. This cleaning substance may simply be water, or it may include detergents. A controller for the cooking device may include a "cleaning" mode, in which controlled amounts of heat are applied to the cleaning substance in order to effectively clean the cooking vessel. Once the vessel is cleaned, the cleaning substance is drained, and the vessel is again filled with a cooking substance.
Although the process of cleaning a cooking device is not particularly complex, problems may still arise. In particular, problems may arise with the application of too much heat to a cleaning substance, especially if the cleaning substance has a boiling point near that of water. If too much heat is applied to this cleaning substance, and the cleaning substance boils, the cooking vessel may be damaged by oxidation or overpressure. This may require the costly replacement of the cooking vessel, heating elements, or sensors. Further, if water or another cleaning substance is not properly drained from the cooking vessel before the cooking vessel is refilled, the cooking substance may be contaminated by the water or cleaning substance. Such contaminated cooking substances may not heat properly and may cause the food products to cook unevenly or inadequately. Further, such contaminated cooking substances may adversely affect the flavor or the food products.
Further, if the cleaning substance is drained from the cooking vessel and not filled with a cooking substance before a heating cycle is initiated, the cooking vessel may overheat, resulting in a risk of fire or equipment damage. In particular, the fryer may be damaged by such "dry firing."
If medium is substantially water, and allowed to reach boiling temperatures, boil over may overflow or boil over and out of the cooking vessel. This too may result in fire or equipment damage. Moreover, such cooking substance boil-over or overflow may result in increased facility maintenance costs, which may further cause a reduction in operating efficiency.